Use of a thiamine antagonist to evaluate the effects of thiamine deficiency on lake trout embryonic development

Abstract

To more fully understand the secondary effects of thiamine deficiency on embryo development of lake trout Salvelinus namaycush, we used an immersion protocol to administer graded doses of the thiamine antagonist oxythiamine (OXY) (e.g., 0, 12.5, 25, 50, 100, 200, and 400mg/L). OXY was administered to eggs of six families at water hardening (fertilization) with the intent that early mortality syndrome (EMS), an acute thiamine deficiency mortality, would only occur at the highest OXY concentration. We assessed the effect of OXY and family on the occurrence of EMS and other embryonic mortality, and alevin growth dynamics up until 2weeks post emergence. EMS reached only 4% at the highest OXY concentration (400mg/L) where there was a significant decline in alevin length and yolkless alevin dry weight but not the dry weight of alevins whose yolk-sac was still attached. The dry weight of the yolk-sac as a percentage of total alevin dry weight was lower than controls at low concentrations of OXY (12.5, 25mg/L), but higher than controls at the highest concentration of OXY (400mg/L). OXY appeared to exert its effect on growth through reduced yolk-sac utilization although the mechanism(s) involved is unknown. Reduced growth and yolk-sac utilization of alevins resulting from thiamine deficiency may contribute to mortality through decreased ability of affected alevins to secure food and avoid predation. We conclude that even for very low EMS, alevin growth effects resulting from thiamine deficiency may pose a significant impediment to lake trout reproduction.